Unity Editor Add Custom MainToolbar button for Build and Run and Enter Playmode

BuildAndPlay.cs

using System.Diagnostics;
using System.IO;
using System.Threading;
using UnityEditor;
using UnityEditor.Toolbars;
using UnityEngine;
using Debug = UnityEngine.Debug;

public class BuildAndPlay
{
    [MainToolbarElement("Tools/BuildsAndPlay", defaultDockPosition = MainToolbarDockPosition.Middle)]
    public static MainToolbarElement BuildAndPlayNow()
    {
        var icon = EditorGUIUtility.IconContent("BuildSettings.Standalone").image as Texture2D;
        var content = new MainToolbarContent(icon);

        return new MainToolbarButton(content, () =>
        {
            // now enter playmode
            EditorApplication.isPlaying = true;


            // call build and run
            BuildPlayerOptions buildPlayerOptions = new BuildPlayerOptions();

            // take scenes from build settings
            var scenes = new System.Collections.Generic.List<string>();
            foreach (var scene in EditorBuildSettings.scenes)
            {
                if (scene.enabled)
                {
                    scenes.Add(scene.path);
                }
            }

            string relativeBuildPath = "../Builds/pc/Project.exe";

            buildPlayerOptions.scenes = scenes.ToArray();
            buildPlayerOptions.locationPathName = relativeBuildPath;
            buildPlayerOptions.target = BuildTarget.StandaloneWindows64;
            buildPlayerOptions.options = BuildOptions.None;
            BuildPipeline.BuildPlayer(buildPlayerOptions);


            // TODO add delay if needed? (exe hangs often?)

            try
            {
                // TODO add amount of clients to run
                // After build is complete, run the built application
                var exepath = Path.Combine(Application.dataPath, "..", "Builds", "pc", "Project.exe");
                Process.Start(exepath);
            }
            catch (System.Exception e)
            {

                Debug.LogException(e);
                throw;
            }
        });
    } // BuildAndPlayNow


} // class